Endocrine Drugs and Medications Q 33
Which drug is used to manage preterm labor by causing smooth muscle relaxation?
A. Oxytocin
B. Prostaglandin
C. Ritodrine
D. Estrogen
Correct Answer: C. Ritodrine
Ritodrine is used to arrest uterine contractions in preterm labor. Tocolysis is effective because it focuses on both delaying and weakening uterine contractions. The pharmacology targets the activity of the myometrium. The myometrium is the smooth muscle in the uterus. Tocolysis is used in the setting of preterm labor. Preterm birth is delivery before 37 weeks gestation and after 20 weeks. To diagnose preterm labor, continued contractions happen during the gestational age range mentioned previously to produce cervical changes.
Option A: Oxytocin is used to stimulate labor. From a physiologic perspective, the myometrium is responsible for the contractional effort of childbirth. Like all smooth muscles, this process is calcium-mediated. The start of a contraction does not require any nerve input nor hormonal stimulus. It begins with a spontaneous depolarization of the cell surface, which opens voltage-gated calcium channels. The influx of calcium into the cells binds to intracellular calmodulin. This new complex activates myosin light chain kinase, an enzyme that phosphorylates myosin light chains, which are located on a critical portion of the myosin heads. The phosphorylation and dephosphorylation of the myosin head cause the continual bridging to actin filaments. This repetitive process results in the myometrium of contraction.
Option B: Prostaglandins can cause vasodilation or vasoconstriction in vascular smooth muscle cells, activate or inhibit platelet aggregation, induce labor, regulate hormones, and decrease intraocular pressure. PGF2 alpha can be applied vaginally or intramuscularly to induce abortion in pregnant patients. In some cases, misoprostol (PGE1) can be used rectally for the treatment of postpartum hemorrhage.
Option D: Estrogen is a steroid hormone associated with the female reproductive organs and is responsible for the development of female sexual characteristics. Estrogen is often referred to the following structures as either estrone, estradiol, and estriol. Of the previously mentioned forms of estrogen, estradiol is the most common form of estrogen hormone for hormone replacement therapy (HRT) in the treatment of symptoms of menopause. In the uterus, estrogen helps to proliferate endometrial cells in the follicular phase of the menstrual cycle, thickening the endometrial lining in preparation for pregnancy.